The present invention relates generally to piston pumps, and more particularly to piston pumps driven by a rotating cam.
Piston pumps are commonly used to move fluids such as oil or grease in a wide range of industrial and automotive applications. Piston pumps driven by a rotating cam pump an approximately constant amount of fluid with each rotation of the cam.
Piston pumps driven by rotating cams comprise three parts: a cam, a piston engaged with the cam, and a cylinder containing the piston. Cams can be circular, elliptical, or irregularly shaped discs, but in all cases exert a force on the piston as the cam rotates. The piston of a piston pump is typically constrained to move along a straight path inside the cylinder, and is retained against an outer circumferential surface of the cam. The cylinder of a piston pump constrains the piston, and provides a pumping chamber into which fluid is drawn, and from which fluid is pumped by movement of the piston. Many pistons are substantially cylindrical shafts, and most cylinders are substantially cylindrical tubes. Piston cylinders include inlet ports which allow fluid to enter the pumping chamber. These ports are typically holes in the sides of the cylinder.
As the cam of a piston pump rotates, the piston is pushed back and forth inside the cylinder with the assistance of a spring, towards and away from the cam. The cam pushes the piston into the cylinder, and the spring returns the piston when the cam retreats. This reciprocating motion of the piston opens and closes at least one port in the piston cylinder by unblocking and blocking the port. While the piston withdraws, fluid flows through the open port into the pumping chamber of the cylinder. When the piston extends, it blocks the port and forces fluid trapped in the pumping chamber out through a pump outlet.
In cam-driven piston pumps, the piston is conventionally aligned with the cam such that the shaft of the piston extends radially outward from the axis of rotation of the cam. This results in the piston pumping for half of the rotation of the cam, and the cylinder filling for the other half of the rotation of the cam. Many cams apply force to pistons by rotating about an eccentrically-located axis. Such cams apply forces to radially oriented pistons which are not entirely along the direction of motion of the piston.